Method of securing workpieces

ABSTRACT

A method of securing at least two workpieces, which includes inserting a bolt shaft through a bore hole formed in each of the workpieces, and applying a sealant to the workpieces. Further, the method includes engaging a locking collar with the bolt shaft such that the locking collar is securely deformed in a locking manner thereby forcing the sealant to uniformly distribute and form a thin surface sealant layer on the bolt shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation application of published U.S.application Ser. No. 10/081,878, filed on Feb. 20, 2002, which claimspriority under 35 U.S.C. § 119 to German Patent Application 101 07952.4, filed on Feb. 20, 2001, the entire disclosure of both which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a method of securing two or morecomponents, i.e. workpieces, with a locking collar, a bolt shaft througha hole in the workpieces and a sealant.

[0004] 2. Background Information

[0005] It is generally known to use lockbolts for forming high-strengthmechanical joints of two or more workpieces, for example in the field ofaircraft manufacturing. The lockbolt is secured in aligned holes throughthe workpieces, which have been sealed or provided with a sealant. Thelockbolt includes a shaft that extends through the holes in theworkpieces, and a bolt head at one end of the shaft, whereby the headlies against the outer surface of one of the workpieces. The other endof the shaft that protrudes out of the opposite side of the otherworkpiece includes a profiled locking portion, onto which is secured alock ring or collar, such as a swageable collar for establishing asecure force-locking and force-transmitting connection. The lockboltfurther includes a break-away portion or pintail portion that isconnected to the locking portion by a predetermined breaking point orso-called break-pin area, for example in the manner of a frangible neck.This break-away portion can be gripped with an appropriate tool, such asa tension-applying tool for forming the mechanically secure connectionand then breaking off the break-away portion.

[0006] A lockbolt of the above described general type is disclosed, forexample, in published European Patent Application EP 0,955,477. Thelockbolt according to this publication has the following structure withthe following components. The lockbolt includes a shaft comprising ashank for penetrating through and closely fitting into the bored holesin the components or workpieces that are to be connected. The boltfurther includes a bolt head for preventing axial movement of thelockbolt within the bored holes in the workpieces. A locking portion orregion of the shaft includes plural circumferentially extending annulargrooves, which are engaged by a swageable locking collar forestablishing a mechanical connection of the lockbolt with theworkpieces. A pintail or break-away portion is connected to the end ofthe locking portion by a break-pin area or frangible neck, which isparticularly located between the above-mentioned circumferential annulargrooves of the locking portion and the pintail. When the locking collaris swaged and coupled onto the grooves of the locking portion, thepintail is released from the shank by breaking the break-pin area.

[0007] Especially according to the above mentioned EP 0,955,477, anO-ring is arranged on the break-pin area or on the pintail, i.e.generally between the locking collar and the free end of the boltopposite the bolt head. The outer diameter of the O-ring is larger thanthe diameter of the shank, so that as the lockbolt, with the 0-ringthereon, is inserted into the bored hole in the workpieces, the O-ringwill wipe any excess undesired sealant within the bored hole and preventthis sealant from reaching and filling into the annular circumferentiallocking grooves. The sealant is supposed to stay on the portion of thelockbolt between the O-ring and the free end of the bolt, i.e. on thebreak-away pintail, without contaminating the grooves of the lockingportion of the bolt.

[0008] The known arrangement of a lockbolt with a sealant-wiping O-ringis intended to prevent the undesired accumulation of sealant from thebore hole of the workpieces into the locking grooves of the bolt. Suchsealant would otherwise have to be manually removed from the groovesbefore the locking collar can be swaged and engaged thereon. If sealantremains in the grooves when the locking collar is to be swaged thereon,then the sealant becomes trapped and encapsulated by the locking collarwithin these closed and continuous circumferential grooves, andtherefore forms a pressurized hydraulic buffer, which prevents theproper complete swaging engagement of the locking collar into thelocking grooves of the bolt.

[0009] In actual practice, while the O-ring wipes some sealant out ofthe bored hole of the workpieces and thus ahead of and away from thelocking grooves of the bolt, some sealant nevertheless still reaches andcontaminates the annular circumferential grooves. Thus, the properfunctionality of the mechanical swaged connection cannot be reliably andcompletely ensured in the event of a remaining contamination of theparts of the bolts. This is especially problematic due to the annularcircumferential configuration of the locking grooves of the lockingportion of the known bolts. Whenever sealant or other contaminant ispresent in such circumferential annular grooves, the sealant orcontaminant becomes sealed and encapsulated in this closed groove by thelocking collar being swaged onto the locking portion of the bolt. Thesealant or contaminant thus forms a pressurized hydraulic buffer betweenthe locking portion of the bolt and the locking collar. As a result, thelocking collar cannot be properly and completely swaged onto the lockingportion of the bolt shank, so that an adequate mechanical holding powercannot be achieved. Moreover, a further disadvantage is that the O-ringsmust be individually installed on the individual lockbolts, and afterthe bolt-securing process, the O-rings must be tediously removed, ifthey have not fallen away by themselves.

SUMMARY OF THE INVENTION

[0010] In view of the above, it is an object of the invention to providea lockbolt of the above described general type, which is improved insuch a manner so as to achieve a sufficient functional security evenwhen the functional area between the locking portion of the bolt and thelocking collar is contaminated with sealant. Another object of theinvention is to simplify the work necessary for securely installing andfastening such a lockbolt. The invention further aims to avoid orovercome the disadvantages of the prior art, and to achieve additionaladvantages, as apparent from the present specification.

[0011] The above objects have been achieved according to the inventionin a lockbolt having a bolt shaft and a bolt head at one end of the boltshaft. The bolt shaft includes a locking portion, and a break-awayportion connected to the locking portion through a predeterminedbreaking point. The bolt itself is arranged further in combination witha locking collar that is mechanically secured, e.g. crimped or swaged,onto the locking portion of the bolt shaft. The circumferential orgenerally cylindrical surface of the locking portion of the bolt shaftis provided with a knurling thereon, especially in the manner of aso-called brilliant or diamond-patterned functional area. The knurlingmay, for example, include an intersecting or criss-crossing pattern ofspiral grooves that respectively spiral in two opposite directionsaround the locking portion of the bolt shaft, and form therebetween aplurality of diamond-shaped knurling peaks bounded by sloping, knurlingflanks. This knurling pattern or surface configuration can be cut,pressed, molded, cast, embossed, or otherwise formed on the surface ofthe locking portion of the bolt shaft. Preferably, the knurling groovesextend at an angle, i.e. in a spiral configuration, from one axial endto the other of the locking portion. A sealant is provided between theknurled surface of the locking portion and the locking collar.

[0012] The knurling of the locking portion of the bolt shaft providesthe necessary mechanical gripping and locking structures onto which thelocking collar is deformed, i.e. crimped or swaged, in order toestablish a secure mechanical connection of the locking collar onto thelocking portion of the bolt shaft, and thereby to securely mechanicallyjoin the workpieces between the bolt head and the locking collar, withthe bolt shaft extending through aligning holes provided in theworkpieces.

[0013] Moreover, the knurling allows the sealant between the lockingcollar and the knurled surface of the locking portion of the bolt shaftto be distributed, and any excessive sealant to be squeezed-out, asfollows. When the shaft of the locking bolt is inserted through thealigned holes of the workpieces, which have been sealed with a sealant,the sealant becomes smeared or wiped onto the shaft of the bolt,including the locking portion thereof. When the locking collar isdeformed and locked onto the knurled surface of the locking portion ofthe bolt shaft, the knurling grooves allow the sealant to becomeuniformly spread out to form a thin surfacial sealant layer or film overthe knurled surface, i.e. between the knurling and the inner surface ofthe locking collar being deformed onto the knurling. Thereby, this thinsealant layer provides an additional sealing and adhesive functionwithout hindering the mechanical swaging or deforming interconnection ofthe locking collar onto the knurled surface of the locking portion ofthe bolt shaft.

[0014] According to further details of embodiments of the invention, thepredetermined breaking point or frangible neck is formed by acircumferentially extending annular groove between the locking portionand the break-away portion of the shaft. Also, the break-away portionpreferably comprises a plurality of parallel circumferentially extendinggrooves thereon, which allow a tool such as a tensioning tool orclamping, squeezing and upsetting tool to be mechanically securedthereon.

[0015] A significant advantage of the invention is that the knurlingprovided on the surface of the locking portion of the bolt shafteffectively prevents the formation of encapsulated chambers, and insteadprovides venting and sealant-escape-paths between the locking portionand the locking collar, as the locking collar is deformed or swaged ontothe locking portion of the bolt shaft. Particularly, the knurlinggrooves provide an outlet for the excess sealant to escape or besqueezed-out from between the locking collar and the locking portion ofthe bolt shaft along these knurling grooves, and also achieves atargeted distribution of a small remaining amount of sealant to form athin sealant layer or film between the locking collar and the lockingportion of the bolt shaft, as follows. During the joining or securingprocess, the locking collar is securely deformed in a force-lockingmanner onto the knurling peaks, but the locking collar preferably andadvantageously does not completely penetrate into and fill the bottom ofthe knurling grooves or the shaft base surface between the knurlingpeaks. This leaves gap channels at the bottom of the knurling grooves,i.e. free gap channels between the knurling base surface and the lockingcollar, in which the sealant can uniformly distribute itself. In thismanner, the formation of an enclosed or encapsulated, pressurizedhydraulic buffer (which would be the case in a continuouscircumferential extending annular groove) is avoided during the swagingdeformation of the locking collar, because the knurling includes spiralgrooves that extend helically in the axial direction so as to interruptand open-up any isolated grooves such as circumferentially extendinggrooves.

[0016] Instead of a knurling pattern including spiral knurling grooves,it is alternatively possible to provide a knurling pattern formed by theintersection of circumferentially extending grooves and axiallyextending grooves. With such a knurling pattern, the axially extendinggrooves provide the venting or sealant-distributing function to preventthe formation of a sealed, encapsulated hydraulic buffer of sealantmaterial enclosed in a continuous circumferentially extending groove. Ageneralized feature of an embodiment of the invention is thus that theknurling pattern includes grooves that extend in a direction having anaxial component, so as to prevent the formation of enclosed cells orhydraulic buffers in which the sealant becomes trapped between the boltshaft surface and the locking collar.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order that the invention may be clearly understood, it willnow be described in connection with example embodiments, with referenceto the accompanying drawings, wherein:

[0018]FIG. 1 is a side view of a first embodiment of a lockboltaccording to the invention;

[0019]FIG. 2 is a side view of the lockbolt of FIG. 1, installed in twosectionally illustrated plate-shaped workpieces that are to be joined,and a sectionally illustrated locking collar arranged on the bolt, at astage before the locking or joining process;

[0020]FIG. 3 is a view similar to that of FIG. 2, at a stage aftercompletion of the joining process and separation of the break-awayportion of the lockbolt; and

[0021]FIG. 4 is a side view of a second embodiment of a lockboltaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] As shown in FIG. 1, a lockbolt 1 includes a flat countersunk head3 mechanically rigidly connected to one end of a generally cylindricalshaft 20. Instead of the countersunk head 3, the lockbolt may have anyother conventionally known head configuration, such as a cylindricalhead, a pan head, a round head, or the like. Adjoining the bolt head 3,the shaft 20 includes a cylindrical shank 2, which transitions through apreferably conically tapering portion 4 into a profiled orsurface-patterned locking portion 5. The surface profiling of thislocking portion 5 comprises a knurling 6 therearound, made up ofknurling peaks 7B bounded by knurling flanks 7, between respectiveadjacent knurling grooves 7A. In this embodiment, the knurling peaks 7Bare essentially diamond-shaped, i.e. having a pyramid shape with afour-sided diamond-shaped base, and the knurling grooves 7A include twosets of grooves respectively extending in opposite spiral directionshelically around the surface of the bolt shaft and intersecting oneanother.

[0023] The locking portion 5 of the bolt shaft 20 is connected through apredetermined breaking point or frangible neck 8 to a break-away portion10 of the bolt shaft 20 that is adapted to have an installation tool(not shown) engaged thereon. In this embodiment, the predeterminedbreaking point or frangible neck 8 is formed by a circumferentiallyextending groove 9. For securely engaging the installation tool onto thebreak-away portion 10 of the lockbolt 1, at least a part of thebreak-away portion 10 is provided with grooves 11, particularly such asthe illustrated parallel circumferentially extending grooves 11.

[0024]FIG. 2 shows the arrangement of the lockbolt 1 during theinstallation process. The lockbolt 1 will cooperate with a cylindricalsleeve-shaped locking collar 16 (which may alternatively have an axiallyshorter ring configuration) to form a mechanically secure connection oftwo workpieces 12 and 13 with each other. The joint and the lockboltwill additionally be sealed by a sealant 18. In this example, theworkpieces 12 and 13 are substantially plate-shaped workpieces. Thesetwo workpieces 12 and 13 are arranged overlapping and surfaciallycontacting each other with respective individual facing surfacesthereof, and are respectively provided with mutually aligned fittingbore holes 14 and 15, through which the shank 2 of the lockbolt 1extends.

[0025] The hole 14 in the workpiece 12 includes a conically taperedcountersink recess, in which the countersunk head 3 of the lockbolt 1 isreceived with the flat surface of the head 3 flush with the outersurface of the workpiece 12. The conically tapering transition portion4, the locking portion 5, the predetermined breaking point 8, and thebreak-away portion 10 of the lockbolt 1 protrude outwardly from theopposite side, i.e. the opposite outer surface of the second workpiece13. The cylindrical sleeve-shaped locking collar 16 is arranged on thebolt shaft 20 so that the conical tapering transition portion 4 as wellas the portion 5 of the bolt shaft 20 are received and surrounded in thebore 17 of the locking collar 16.

[0026] In order to form a tight seal at the location of this joint, i.e.through the holes 14 and 15 and the arrangement of the locking bolt 1, asealant 18 is applied between the workpieces 12 and 13, and/or in theholes 14 and 15 of the workpieces 12 and 13, before or together with theinsertion of the shaft 20 of the lockbolt 1 into the holes 14 and 15.The sealant 18 may even be applied directly to the locking bolt 1 whenit is inserted into the holes 14 and 15. In any event, during thisso-called “wet assembly” of the lockbolt 1 into the holes 14 and 15 ofthe workpieces 12 and 13, contamination in the form of deposits orexcess amounts of the sealant 18 will be accumulated on the knurling 6,and particularly in the knurling grooves 7A between the knurling flanks7. According to the invention, it is not necessary to remove the sealant18 from this area before arranging the locking collar 16 thereon, butrather the sealant 18 at this location will purposely serve anadditional sealing and adhesive function between the lockbolt 1 and thelocking collar 16.

[0027]FIG. 3 shows the completed, mechanically secured and sealedconnection of the two workpieces 12 and 13 after completion of the boltsetting and joining process. An installation tool (which is not shown)has been set and engaged onto the break-away portion 10 and exerted acompression load onto the locking collar 16, such that the lockingcollar 16 has been swaged into a deformed condition 19 in such a mannerso that it is engaged and locked in a force-locking manner onto thelocking portion 5 of the lockbolt 1. While the locking collar 16 isbeing deformed into the deformed condition 19, simultaneously, thesealant 18 present within the bore 17 of the locking collar 16, 19 isbeing squeezed and spread-out along the knurling 6, and especially so asto form a thin surfacially extending sealant layer or film along theknurling flanks 7. The sealant 18 does not become trapped orencapsulated between the locking collar 16, 19 and the locking portion5, because the knurling 6 (and especially the 30 knurling grooves 7A)allow the sealant 18 to be spread out in the axial direction. Any excessamount of sealant 18 is squeezed-out or exuded as shown by referencenumber 18′ at the open axial end of the locking collar 16, 19, whichcommunicates with the atmosphere around the lockbolt. In this manner,the resulting thin uniform layer of sealant 18 does not hinder themechanical swaging of the locking collar 16, 19 onto the knurling 6, butinstead actually provides an additional adhesive bonding and sealingfunction therebetween.

[0028] As further indicated in FIG. 3, at the end of the joiningprocess, the assembly tool is used to separate the break-away portion 10from the locking portion 5 of the lockbolt 1 at the frangible neck orbreaking point 8. For example, the tool engages the grooves 11, and isthen used to deflect and/or twist and/or pull the break-away portion 10until it is simply broken off at the breaking point 8.

[0029]FIG. 4 shows a second example embodiment of a lockbolt 1 that isgenerally similar to that of FIG. 1, except that the knurling 6 has adifferent configuration. In this embodiment of FIG. 4, the knurling 6includes square or rectangular knurling peaks 7B formed between a firstset of circumferential knurling grooves 7A and a second set of axialknurling grooves 7A. The two sets of grooves intersect each other.Thereby, the axially extending grooves 7A provide for the escape orsqueezing-out and distributing of the sealant 18 in the manner asdescribed above in connection with FIG. 3. Thus, once again in theembodiment of FIG. 4, the sealant 18 will form a distributed thinsealant layer between the deformed locking collar and the knurling,which does not hinder the swaging engagement therebetween, but ratherprovides an additional adhesive bonding and sealing functiontherebetween. In this context, a “thin” layer is one that issufficiently thin so that it does not hinder the mechanical swagingengagement of the collar onto the locking portion.

[0030] Although the invention has been described with reference tospecific example embodiments, it will be appreciated that it is intendedto cover all modifications and equivalents within the scope of theappended claims. It should also be understood that the presentdisclosure includes all possible combinations of any individual featuresrecited in any of the appended claims.

What is claimed is:
 1. A method of securing at least two workpieces,comprising: inserting a bolt shaft through a bore hole formed in each ofthe at least two workpieces; applying a sealant to the at least twoworkpieces; and engaging a locking collar with the bolt shaft such thatthe locking collar is securely deformed in a locking manner therebyforcing the sealant to uniformly distribute and form a thin surfacesealant layer on the bolt shaft.
 2. The method according to claim 1,wherein the applying step applies the sealant to the two workpiecesbefore the inserting step inserts the bolt shaft into the bore hole ofeach of the at least two workpieces.
 3. The method according to claim 1,wherein the applying step applies the sealant directly to the bolt shaftbefore the inserting step inserts the bolt shaft into the bore hole ofeach of the at least two workpieces.
 4. The method according to claim 1,wherein the bolt shaft has a locking portion including a plurality ofgrooves around a surface of the bolt shaft and a plurality of peaks atleast some having a parallelogram shape and being disposed between theplurality of grooves, and wherein the sealant is uniformly distributedvia the plurality of grooves around the surface of the bolt shaft whenthe engaging step engages the locking collar with the bolt shaft.
 5. Themethod according to claim 4, wherein the plurality of grooves extend inspiral directions helically around the surface of the bolt shaft.
 6. Themethod according to claim 4, wherein the plurality of grooves include afirst group of spiral grooves that respectively extend in a clockwisespiral direction and a second group of spiral grooves that respectivelyextend in a counterclockwise spiral direction and intersect with saidfirst group of spiral grooves.
 7. The method according to claim 4,wherein the plurality of grooves include a plurality of first groovesextending in a circumferential direction of the bolt shaft and aplurality of second grooves extending in a direction parallel to thecircumferential direction such that the first and second groovesintersect with each other
 8. The method according to claim 4, whereinthe parallelogram shape is a diamond parallelogram shape.
 9. The methodaccording to claim 4, wherein the parallelogram shape is a pyramid shapewith a four-sided base.
 10. The method according to claim 4, wherein theparallelogram shape is a square or rectangular shape.
 11. The methodaccording to claim 1, wherein when the engaging step engages the lockingcollar with the bolt shaft, excess sealant is squeezed out a second endof the bolt shaft via at least one groove on a surface of the bolt shaftthat opens to an outside at an axial end of the locking portion.
 12. Themethod according to claim 4, wherein respective ones of said pluralityof grooves intersect with one another so that all of said plurality ofgrooves are interconnected and intercommunicated with each other, andwherein at least one of said plurality of grooves extends to and opensat an open groove end at an axial end of said locking portion along anaxial direction of the bolt shaft such that excess sealant is squeezedout the open groove.
 13. The method according to claim 4, wherein saidlocking portion excludes all annular circumferential grooves.
 14. Themethod according to claim 4, wherein each of the plurality of peaksincludes a parallelogram shape.
 15. The method according to claim 4,further comprising: breaking off a break-away portion of the bolt shaftthat is connected to said locking portion.
 16. The method according toclaim 15, wherein the breaking step breaks off the break-away portion bybreaking a constricted neck encircled by a circumferential groove.